Minimum viable product for the Physics Derivation Graph

I've been looking for ways to pare down the tasks that I face in building the Physics Derivation Graph. Defining a minimum viable product for delivery would help prioritize what I work on.

Although the d3js-based interactive graphs are neat, they don't provide much value. The static PNGs of derivations are not as sexy, but they are easier to navigate. The PNGs are the minimum viable product.

As far as storage formating, I think the "file per expression" approach is still the best option, compared to CSV, XML, and MathML.

Thus, the MVP needs to be able to generate PNGs of a graph from derivations stored in the "file per expression" method.

Generating a file per expression is a tedious task that both limits scalability and could introduce errors if done manually. The command-line based interactive user prompt is a useful tool that addresses both concerns.

The interactive user prompt is a potential time sink. Minimum functionality is user should be able to enter a new derivation and write results to file.
Do not include ability to edit existing derivations, or to link existing derivations by deconflicting expressions with different identifiers.

Task 1: generate graph PNG from file per expressions
Task 2: generate file per expression from interactive prompt
Task 3: convert from interactive command-line prompt to web-based prompt